1. 07 Dec, 2011 1 commit
  2. 02 Nov, 2011 2 commits
    • Andrea Arcangeli's avatar
      thp: share get_huge_page_tail() · b35a35b5
      Andrea Arcangeli authored
      This avoids duplicating the function in every arch gup_fast.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: David Gibson <david@gibson.dropbear.id.au>
      Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
      Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
      Cc: David Miller <davem@davemloft.net>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Andrea Arcangeli's avatar
      mm: thp: tail page refcounting fix · 70b50f94
      Andrea Arcangeli authored
      Michel while working on the working set estimation code, noticed that
      calling get_page_unless_zero() on a random pfn_to_page(random_pfn)
      wasn't safe, if the pfn ended up being a tail page of a transparent
      hugepage under splitting by __split_huge_page_refcount().
      He then found the problem could also theoretically materialize with
      page_cache_get_speculative() during the speculative radix tree lookups
      that uses get_page_unless_zero() in SMP if the radix tree page is freed
      and reallocated and get_user_pages is called on it before
      page_cache_get_speculative has a chance to call get_page_unless_zero().
      So the best way to fix the problem is to keep page_tail->_count zero at
      all times.  This will guarantee that get_page_unless_zero() can never
      succeed on any tail page.  page_tail->_mapcount is guaranteed zero and
      is unused for all tail pages of a compound page, so we can simply
      account the tail page references there and transfer them to
      tail_page->_count in __split_huge_page_refcount() (in addition to the
      While debugging this s/_count/_mapcount/ change I also noticed get_page is
      called by direct-io.c on pages returned by get_user_pages.  That wasn't
      entirely safe because the two atomic_inc in get_page weren't atomic.  As
      opposed to other get_user_page users like secondary-MMU page fault to
      establish the shadow pagetables would never call any superflous get_page
      after get_user_page returns.  It's safer to make get_page universally safe
      for tail pages and to use get_page_foll() within follow_page (inside
      get_user_pages()).  get_page_foll() is safe to do the refcounting for tail
      pages without taking any locks because it is run within PT lock protected
      critical sections (PT lock for pte and page_table_lock for
      The standard get_page() as invoked by direct-io instead will now take
      the compound_lock but still only for tail pages.  The direct-io paths
      are usually I/O bound and the compound_lock is per THP so very
      finegrined, so there's no risk of scalability issues with it.  A simple
      direct-io benchmarks with all lockdep prove locking and spinlock
      debugging infrastructure enabled shows identical performance and no
      overhead.  So it's worth it.  Ideally direct-io should stop calling
      get_page() on pages returned by get_user_pages().  The spinlock in
      get_page() is already optimized away for no-THP builds but doing
      get_page() on tail pages returned by GUP is generally a rare operation
      and usually only run in I/O paths.
      This new refcounting on page_tail->_mapcount in addition to avoiding new
      RCU critical sections will also allow the working set estimation code to
      work without any further complexity associated to the tail page
      refcounting with THP.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Reported-by: default avatarMichel Lespinasse <walken@google.com>
      Reviewed-by: default avatarMichel Lespinasse <walken@google.com>
      Reviewed-by: default avatarMinchan Kim <minchan.kim@gmail.com>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: David Gibson <david@gibson.dropbear.id.au>
      Cc: <stable@kernel.org>
      Cc: <stable@vger.kernel.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  3. 14 Jan, 2011 3 commits
  4. 03 Feb, 2010 1 commit
  5. 20 Jun, 2009 1 commit
    • Linus Torvalds's avatar
      x86: don't use 'access_ok()' as a range check in get_user_pages_fast() · 7f818906
      Linus Torvalds authored
      It's really not right to use 'access_ok()', since that is meant for the
      normal "get_user()" and "copy_from/to_user()" accesses, which are done
      through the TLB, rather than through the page tables.
      Why? access_ok() does both too few, and too many checks.  Too many,
      because it is meant for regular kernel accesses that will not honor the
      'user' bit in the page tables, and because it honors the USER_DS vs
      KERNEL_DS distinction that we shouldn't care about in GUP.  And too few,
      because it doesn't do the 'canonical' check on the address on x86-64,
      since the TLB will do that for us.
      So instead of using a function that isn't meant for this, and does
      something else and much more complicated, just do the real rules: we
      don't want the range to overflow, and on x86-64, we want it to be a
      canonical low address (on 32-bit, all addresses are canonical).
      Acked-by: default avatarIngo Molnar <mingo@elte.hu>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  6. 19 Jun, 2009 1 commit
    • Ingo Molnar's avatar
      perf_counter, x86: Improve interactions with fast-gup · 0c871971
      Ingo Molnar authored
      Improve a few details in perfcounter call-chain recording that
      makes use of fast-GUP:
      - Use ACCESS_ONCE() to observe the pte value. ptes are fundamentally
        racy and can be changed on another CPU, so we have to be careful
        about how we access them. The PAE branch is already careful with
        read-barriers - but the non-PAE and 64-bit side needs an
        ACCESS_ONCE() to make sure the pte value is observed only once.
      - make the checks a bit stricter so that we can feed it any kind of
        cra^H^H^H user-space input ;-)
      Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
  7. 15 Jun, 2009 1 commit
  8. 10 Apr, 2009 1 commit
  9. 29 Oct, 2008 1 commit
    • Harvey Harrison's avatar
      x86: two trivial sparse annotations · 9352f569
      Harvey Harrison authored
      Impact: fewer sparse warnings, no functional changes
      arch/x86/kernel/vsmp_64.c:87:14: warning: incorrect type in argument 1 (different address spaces)
      arch/x86/kernel/vsmp_64.c:87:14:    expected void const volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:87:14:    got void *[assigned] address
      arch/x86/kernel/vsmp_64.c:88:22: warning: incorrect type in argument 1 (different address spaces)
      arch/x86/kernel/vsmp_64.c:88:22:    expected void const volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:88:22:    got void *
      arch/x86/kernel/vsmp_64.c:100:23: warning: incorrect type in argument 2 (different address spaces)
      arch/x86/kernel/vsmp_64.c:100:23:    expected void volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:100:23:    got void *
      arch/x86/kernel/vsmp_64.c:101:23: warning: incorrect type in argument 1 (different address spaces)
      arch/x86/kernel/vsmp_64.c:101:23:    expected void const volatile [noderef] <asn:2>*addr
      arch/x86/kernel/vsmp_64.c:101:23:    got void *
      arch/x86/mm/gup.c:235:6: warning: incorrect type in argument 1 (different base types)
      arch/x86/mm/gup.c:235:6:    expected void const volatile [noderef] <asn:1>*<noident>
      arch/x86/mm/gup.c:235:6:    got unsigned long [unsigned] [assigned] start
      Signed-off-by: default avatarHarvey Harrison <harvey.harrison@gmail.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
  10. 13 Oct, 2008 1 commit
  11. 29 Jul, 2008 1 commit
  12. 26 Jul, 2008 2 commits
    • Nick Piggin's avatar
      x86: support 1GB hugepages with get_user_pages_lockless() · 652ea695
      Nick Piggin authored
      Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andi Kleen <andi@firstfloor.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Nick Piggin's avatar
      x86: lockless get_user_pages_fast() · 8174c430
      Nick Piggin authored
      Implement get_user_pages_fast without locking in the fastpath on x86.
      Do an optimistic lockless pagetable walk, without taking mmap_sem or any
      page table locks or even mmap_sem.  Page table existence is guaranteed by
      turning interrupts off (combined with the fact that we're always looking
      up the current mm, means we can do the lockless page table walk within the
      constraints of the TLB shootdown design).  Basically we can do this
      lockless pagetable walk in a similar manner to the way the CPU's pagetable
      walker does not have to take any locks to find present ptes.
      This patch (combined with the subsequent ones to convert direct IO to use
      it) was found to give about 10% performance improvement on a 2 socket 8
      core Intel Xeon system running an OLTP workload on DB2 v9.5
       "To test the effects of the patch, an OLTP workload was run on an IBM
        x3850 M2 server with 2 processors (quad-core Intel Xeon processors at
        2.93 GHz) using IBM DB2 v9.5 running Linux 2.6.24rc7 kernel.  Comparing
        runs with and without the patch resulted in an overall performance
        benefit of ~9.8%.  Correspondingly, oprofiles showed that samples from
        __up_read and __down_read routines that is seen during thread contention
        for system resources was reduced from 2.8% down to .05%.  Monitoring the
        /proc/vmstat output from the patched run showed that the counter for
        fast_gup contained a very high number while the fast_gup_slow value was
      (fast_gup is the old name for get_user_pages_fast, fast_gup_slow is a
      counter we had for the number of times the slowpath was invoked).
      The main reason for the improvement is that DB2 has multiple threads each
      issuing direct-IO.  Direct-IO uses get_user_pages, and thus the threads
      contend the mmap_sem cacheline, and can also contend on page table locks.
      I would anticipate larger performance gains on larger systems, however I
      think DB2 uses an adaptive mix of threads and processes, so it could be
      that thread contention remains pretty constant as machine size increases.
      In which case, we stuck with "only" a 10% gain.
      The downside of using get_user_pages_fast is that if there is not a pte
      with the correct permissions for the access, we end up falling back to
      get_user_pages and so the get_user_pages_fast is a bit of extra work.
      However this should not be the common case in most performance critical
      [akpm@linux-foundation.org: coding-style fixes]
      [akpm@linux-foundation.org: build fix]
      [akpm@linux-foundation.org: Kconfig fix]
      [akpm@linux-foundation.org: Makefile fix/cleanup]
      [akpm@linux-foundation.org: warning fix]
      Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
      Cc: Dave Kleikamp <shaggy@austin.ibm.com>
      Cc: Andy Whitcroft <apw@shadowen.org>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Andi Kleen <andi@firstfloor.org>
      Cc: Dave Kleikamp <shaggy@austin.ibm.com>
      Cc: Badari Pulavarty <pbadari@us.ibm.com>
      Cc: Zach Brown <zach.brown@oracle.com>
      Cc: Jens Axboe <jens.axboe@oracle.com>
      Reviewed-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>